Page 246 - Adsorbents fundamentals and applications

9

CARBON NANOTUBES,

PILLARED CLAYS,

AND POLYMERIC RESINS

Three different types of sorbents are included in this chapter. Among them, poly-
meric resins and their derivatives have been used commercially for adsorption
and ion exchange. The other two types have not been used commercially. How-
ever, they each have interesting and unique adsorption properties and are subjects
of active research. For these reasons, they are included in this chapter.

9.1. CARBON NANOTUBES

The discovery of fullerenes and carbon nanotubes has opened a new chapter in
carbon chemistry. Carbon nanotubes, in particular, hold tremendous potential for
applications because of their unique properties, such as high thermal and electrical
conductivities, high strengths, and high stiffness (chapters in Dresselhaus et al.,
2001). Potential applications include: electron microscope tips, field and light
emitters, microelectronic devices, nanoprobes and nanosensors, high Li capacitors
for rechargeable Li batteries, composite materials, and replacing Si as the smallest
computer chips.
A vast and rapidly growing volume of literature exists on carbon nanotubes.
The coverage and discussion on this subject here will be limited to their syntheses,
characterization, special adsorption properties, and potential applications as sor-
bents. Some terminologies are first defined. Single-wall nanotubes are denoted by
SWNT, whereas MWNT stands for multiwall nanotubes. A SWNT is a seamless
cylinder wrapped by a graphite sheet (or graphene sheet). The hexagonal honey-
comb lattice of the graphene sheet can be oriented in many possible directions
relative to the axis of the tube. Depending on the relative orientation (and size),
a SWNT can be metallic or semiconducting (Louie, 2001; Yao et al., 2001). The
relative orientation is referred to as the “helicity,” expressed by a set of indices

Adsorbents: Fundamentals and Applications, Edited By Ralph T. Yang
ISBN 0-471-29741-0 Copyright  2003 John Wiley & Sons, Inc.

231